Secuno
ENNL
Book demo

CVE-2026-20039

Cisco Secure Firewall Threat Defense vulnerability

8.6 HIGHEPSS 0.36%
  1. Published4 Mar 2026

Description

A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to ineffective memory management of the VPN web server. An attacker could exploit this vulnerability by sending a large number of crafted HTTP requests to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeChanged
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

Affected products

Cisco Secure Firewall Threat Defense≥ 6.4.0 < 7.0.9 · ≥ 7.1.0 < 7.2.10 · ≥ 7.3.0 < 7.4.3 · ≥ 7.6.0 < 7.6.1
Cisco Adaptive Security Appliance Software≥ 9.12.1 < 9.16.4.84 · ≥ 9.17.1 < 9.18.4.57 · ≥ 9.19.1 < 9.20.3.16 · ≥ 9.22.1.1 < 9.22.2.4

Remediation

Fixed in
Cisco Secure Firewall Threat Defense≥ 7.0.9
Cisco Adaptive Security Appliance Software≥ 9.16.4.84

References

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

CVE-2026-203498.6
A vulnerability in the Remote Access SSL VPN service for Cisco Secure Firewall Adaptive…

Frequently asked

Is CVE-2026-20039 being actively exploited?

CVE-2026-20039 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.36%.

How severe is CVE-2026-20039?

CVE-2026-20039 has a CVSS 3.1 base score of 8.6, rated high. EPSS estimates a 0.36% probability of exploitation.

Which products are affected by CVE-2026-20039?

Affected products include Cisco Secure Firewall Threat Defense, Cisco Adaptive Security Appliance Software.

How do I fix CVE-2026-20039?

Upgrade affected software to a fixed version, for example Cisco Secure Firewall Threat Defense 7.0.9, Cisco Adaptive Security Appliance Software 9.16.4.84 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-20039 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

See how prioritisation worksBook a demo

Get Patch this first every Monday

Five vulnerabilities that matter this week, ranked on real exploitation. Plain language, one email, no spam.

You can unsubscribe with one click from every issue. We handle your details as described in our privacy policy.

Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.